INTERNAL-REFLECTION FLASH-PHOTOLYSIS STUDY OF THE PHOTOCHEMISTRY OF EOSIN AT TIO2 SEMICONDUCTOR ELECTRODES

It is shown that the photoelectrochemical data on eosin Y sensitized TiO2 single-crystal electrodes cannot be interpreted unambiguously without concomitant data from flash photolysis measurements on this system. By use of a combination of internal reflection spectroscopy and laser flash photolysis, electron exchange with TiO2 was observed for the excited singlet state, the triplet state, and the cation radical of the dye. With a temporal resolution of 100 ns, the kinetics of the charge transfer are compared with those of the dye in solution and used to interpret the photoelectrochemistry of the dye at the electrode. Spectroscopic evidence revealed photocurrent production by the triplet state and a reduction of the eosin cation radical by electrons from the TiO2 conduction band and by hydroquinone.